The invention relates to imaging systems using solid state sensors for detecting multiple picture elements, including optical code imagers and cameras. Aspects of the invention are particularly useful in linear sensor-based and two-dimensional sensor-based, handheld code readers.
Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term xe2x80x9cbar codexe2x80x9d is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as xe2x80x9coptical code readersxe2x80x9d of which bar code scanners are one type. Optical code readers are used in both fixed or portable installations in many diverse environments such as in stores for check-out services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target bar code from a printed listing of many bar codes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a handheld sensor which is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional bar code symbols. The bar code is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional bar code is the UPC/EAN code used to identify, for example, product inventory.
Bar codes can be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of cells or photo sensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a two dimensional or area charge coupled device (CCD) and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view. A one-dimensional linear array of photodiodes is also known for use in detecting a bar code reflection image. See, e.g., U.S. Pat. No. 6,138,915 to Danielson et al.
It is known in the art to use a CCD photo detector and objective lens assembly in an optical code reader. In the past, such systems have employed complex objective lens assemblies originally designed for use in relatively expensive video imaging systems. Such systems may have a single sharp focus and a limited depth of field, which along with conventional aiming, illumination and signal processing and decoding algorithms, limits the versatility and working range of the system.
Other known imaging systems are designed primarily for reading optical codes. Such reading systems involve the assembly and alignment of several small parts. These parts may include a lens, an aperture and a 2D optical detector array such as a CCD chip. Such a structure is illustrated, for example, in U.S. patent application Ser. No. 09/096,578 for Imaging Engine and Method for Code Readers to Correa et al. filed Jun. 12, 1998 and assigned to Symbol Technologies, Inc. The Correa et al. application is hereby incorporated by reference herein.
It is an object of the present invention to further reduce the expense and difficulty associated with providing an optical code reading imaging system.
It is known to provide illumination in optical code readers by employing illuminating devices to supplement ambient light. For example, U.S. Pat. No. 5,703,349 discloses an illumination module comprised of two lines of illuminating LEDs and lens cells. The above mentioned Correa et al. patent application also discloses an illumination system for a hand held optical code imager.
Existing one-dimensional imaging systems utilize off-the-shelf linear CCD detectors. A typical linear detector contains a few thousand pixels and has a total image length of about 28 mm. The focal length for a system using such a detector is approximately 38 mm assuming a field of view of 40 degrees. With a 0.4 mm wide by 6.2 mm high aperture the effective F-number (for light throughput) of the system is 21.4. Significant illumination is required for reasonable performance with such a system, and the device cannot be miniaturized.
It is an object of the present invention to provide an imaging optical code reader which is operable under normal ambient light conditions with little or no supplemental illumination.
It is a further object of the present invention to provide a miniaturized imager with a one-dimensional solid state sensor.
It is a further object of the present invention to provide a miniaturized imager with a two-dimensional solid state sensor.
These and other objects and features of the invention will be apparent from this written description and drawings.
The present invention relates to methods and apparatus useful in imaging optical code readers and camera systems. Techniques are disclosed which are applicable to the design of imaging engines, imaging lenses, apertures, illumination devices and solid state die packages for code readers and cameras of various types.
In a preferred embodiment of the present invention, an imaging apparatus for an optical code reader may be based on a solid state photo sensor, including an array of photo sensor cells for producing electronic signals corresponding to a one-dimensional or two-dimensional array of pixel information for a field of view. In preferred embodiments, the image sensor is a CMOS device, it being understood that other solid state image sensors may be used for the purpose such as CCD (charge coupled device), CMD (charge modulated device) or CID (charge injection device) sensors. At least one lens is provided for focusing light incident on the image sensor. The lens may be part of an injection molded package of the image sensor. An aperture may also be formed in the molded package.
In preferred embodiments a one-dimensional solid state photo sensor may be employed. The term xe2x80x9cone-dimensionalxe2x80x9d is intended to include linear (either curved, segmented or straight lines of sensors cells). Preferred photo sensors have a relatively low number of cells for example about 1000 (e.g. a 1024 cell array) or about 500 (e.g. a 512 cell array).
The system employs an optical assembly (typically an objective lens and aperture) in focusing light from a target optical code symbol on the photo sensor. Advantageously, the optical assembly has an F-number less than 8, preferably less than 5, more preferably less than about 3. An electronic digitizer may be implemented with a microprocessor and software for converting electrical signals to bit content for the target symbol. In preferred embodiments the digitizer is sufficiently powerful to extract bit content from a target symbol where the number of modules represented in the image focused on the photo sensor is less than or equal to the number of cells of the photo sensor.
The system may be particularly adapted to read pre-aligned conventional one-dimensional bar codes by employing an array of rectangular shaped sensor cells and by employing an elongated aperture such as a cats-eye shaped aperture.
The foregoing techniques may be employed to provide a miniature package having, for example, a focal length less than 5 mm and an overall volume of less than one cubic centimeter.
The present invention also includes techniques for efficiently and inexpensively fabricating an imager optical package containing a solid state photo sensor. According to this technique, a solid state photo sensor such as a one-dimensional sensor die is electrically and mechanically bonded to a lead frame. The sensor and a portion of the lead frame is located in a first mold cavity while injecting a fluid, electrically insulating material into the cavity. The fluid is substantially transparent to incident light to be detected by the photo sensor, for example, visible light, IR light and UV light. The mold cavity includes a region or surface for forming an external lens surface for the package. The transparent material is allowed to solidify into a transparent body which embeds or encapsulates the solid state photo sensor and protects it from environmental damage, while also focusing incident light onto it. In preferred embodiments a shell of opaque material may be injection molded around the transparent body. An aperture may be formed in the opaque shell during the molding process.
The foregoing sensors and techniques may be used in code readers such as those described in U.S. patent application Ser. No. 20030029915 filed on the same date as this application entitled Omnidirectional Linear Sensor-Based Code Reading Engines to Barkan and Patel, assigned to Symbol Technologies, Inc. and hereby incorporated by reference herein.
The foregoing is intended as a convenient summary of the present disclosure. The aspects of the invention sought to be protected are set forth in the claims.